Interest in omega-3 fatty acids, high in fish oil, stems in part from studies indicating that populations with high fish consumption have lower mortality from CHD. These populations demonstrate reduced VLDL-triglycerides and LDL-cholesterol. It is believed that the lipid-lowering effects are due to a decrease in hepatic VLDL synthesis, but the mechanism for this action is not known. This research will test a working hypothesis that omega-3 fatty acids decrease VLDL synthesis through a direct inhibition of fatty acid synthesis with subsequent elevation of fatty acid oxidation and a resulting diversion of acyl-CoA away from triglyceride synthesis. A corollary to this hypothesis is that omega-3 fatty acids also cause an adaptive decrease in the sensitivity of carnitine palmitoyltransferase I to inhibition by malony1-CoA, and an increase in the capacity for peroxisomal fatty acid oxidation. This hypothesis can potentially explain the reduction in VLDL-triglycerides and cholesterol and, at least in part, the reduction in LDL-cholesterol. In addition, experiments are designed to investigate the potential modulation of these effects by other dietary components. The proposed experiments have three specific objectives. 1) Initial experiments will compare the utilization and short-term metabolic effects of palmitic acid, linoleic acid, eicosapentaenoic acid (C20:5 omega- 3), and docosahexaenoic acid (C22:6 omega-3) in isolated hepatocytes plus or minus insulin (and in some cases plus or minus indomethacin, a prostaglandin synthesis inhibitor). Parameters to be measured are: 14C incorporation into fatty acid oxidation products and triglycerides from exogenous (1-14C) fatty acids; 3H incorporation into fatty acids, cholesterol and triglycerides (from de novo synthesized fatty acid) from 3H2O; and malonyl-CoA. The contribution of peroxisomal oxidation and the structural characteristics of the omega-3 fatty acid responsible for these effects will be determined. 2) Short-term effects of EPA on the utilization of other fatty acids will be determined. 3) Finally, the long-term adaptive effects of fish oil consumption on hepatic lipid metabolism will be investigated. The significance of this research is that the results may provide potentially useful information concerning the dietary management of CHD.